Insole and foot orthotics made of shape memory material (smm) three-dimensional spacer fabrics

ABSTRACT

A shoe insole comprising:
         a spacer fabric comprising a bottom layer, a top layer, and a plurality of interconnecting filaments extending between said bottom layer and said top layer;   wherein at least one of said bottom layer, said top layer and said plurality of interconnecting filaments comprise a shape memory material.

REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

This patent application:

(i) is a continuation-in-part of pending prior U.S. patent application Ser. No. 13/843,656, filed Mar. 15, 2013 by Matthew Fonte et al. for DYNAMIC POROUS COATING FOR ORTHOPEDIC IMPLANT (Attorney's Docket No. FONTE-15171824), which patent application (a) is a continuation-in-part of prior U.S. patent application Ser. No. 13/764,188, filed Feb. 11, 2013 by Matthew Fonte et al. for POROUS COATING FOR ORTHOPEDIC IMPLANT UTILIZING POROUS, SHAPE MEMORY MATERIALS (Attorney's Docket No. FONTE-15), which patent application claims benefit of prior U.S. Provisional Patent Application Ser. No. 61/596,900, filed Feb. 09, 2012 by Matthew Fonte et al. for POROUS, SHAPE MEMORY MATERIAL, ORTHOPEDIC IMPLANT COATING (Attorney's Docket No. FONTE-15 PROV); (b) claims benefit of prior U.S. Provisional Patent Application Ser. No. 61/612,496, filed Mar. 19, 2012 by Matthew Fonte et al. for POROUS, SHAPE MEMORY MATERIAL, ORTHOPEDIC IMPLANT COATING (Attorney's Docket No. FONTE-17 PROV); (c) claims benefit of prior U.S. Provisional Patent Application Ser. No. 61/661,086, filed Jun. 18, 2012 by Matthew Fonte et al. for “DYNAMIC” ORTHOPEDIC COATINGS MADE OF SPACER FABRIC (Attorney's Docket No. FONTE-18 PROV); and (d) claims benefit of prior U.S. Provisional Patent Application Ser. No. 61/738,574, filed Dec. 18, 2012 by Matthew Fonte et al. for POROUS, SHAPE MEMORY MATERIAL, ORTHOPEDIC IMPLANT COATING (Attorney's Docket No. FONTE-24 PROV);

(ii) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/668,732, filed Aug. 06, 2012 by Matthew Fonte et al. for SHOE INSOLE AND FOOT ORTHOTICS MADE OF SHAPE MEMORY MATERIAL THREE-DIMENSIONAL SPACER FABRICS (Attorney's Docket No. FONTE-20 PROV); and

(iii) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/671,129, filed Aug. 13, 2012 by Matthew Fonte et al. for SUPERELASTIC THREE-DIMENSIONAL SPACER FABRIC USING SHAPE MEMORY MATERIALS (Attorney's Docket No. FONTE-21 PROV).

The eight (8) above-identified patent applications are hereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to footwear in general, and more particularly to the methods and apparatus for better absorbing shock and distributing forces in footwear.

BACKGROUND OF THE INVENTION

During running, loads equaling 1.5 to 5 times body weight are repetitively absorbed through each leg. It has been suggested that this repetitive loading and associated impact shocks cause microtrauma to the underlying tissues and may eventually cause enough damage to impair function. Some common overuse injuries resulting from this repeated microtrauma include stress fractures, shin splints, and plantar fasciitis. The use of cushioned or shock-absorbing insoles has been suggested as a mechanism to reduce the impact forces associated with running, thereby protecting against these overuse injuries.

The insole is the inside part of the shoe that runs underneath the bottom or sole of the foot. Insoles can usually be easily removed, and wearers will sometimes replace the manufacture's insole with specialty insoles purchased separately. Insoles are also sometimes referred to as footbeds, inner soles or innersoles. Orthotics are a type of insert or footbed that are specifically designed for the wearer's foot and provide customized support to the foot by distributing pressure or re-aligning foot joints while standing, walking or running. See FIG. 1, which shows insoles 5 which may be used in a running shoe.

Different locations of the insole serve to cushion and support different regions of the foot. By adjusting the material properties and material thickness along the length of the insole, the insole can be designed to provide additional support for the ball of the foot, the arch of the foot, and/or the heel of the foot. See FIG. 2, which shows a running shoe 10 having a multi-ply insole 5, wherein the multi-ply insole 5 includes a metatarsal bar 15 which relieves pressure of the ball of the foot, a medial arch 20 which provides support for weak arches, and a cupped heel 25 for providing foot and ankle stability and enhanced balance.

Polymeric foams and elastomers are frequently used in shoes to provide shock-absorbing and pressure-distributing functions beneath the foot. Cushioning can be defined as the ability of the insole material to conform elastically to the shape of the foot and distribute pressure while standing, walking or running. Cushioning energy, expressed in milli-Joules, is the energy that is absorbed by the insole during a single compression at a certain pressure. A test method for determining cushioning energy has been developed by the SATRA Institute, “Physical Test Method PM159, Cushioning Properties”. The American Society for Testing and Materials (ASTM) has published ASTM F1976-06 which describes test methods for determining the impact attenuation properties of athletic shoes. The ASTM test measures force versus displacement when an applied load of 44.2 in.-lbf or 61.9 in.-lbf is applied to a shoe insole.

Common materials that are used in insoles to improve cushioning energy include foam rubbers such as latex and cellular polymers such as polyethylene (PE), ethylene vinyl acetate (EVA), polyurethane (PU), and polyvinyl chloride (PVC). Additionally solid materials such as viscoelastic polymers and natural cork are also used effectively at cushioning. Ethylene vinyl acetate (EVA) offers good cushioning and shock absorption, but tends to suffer high compression set, meaning that these properties deteriorate rapidly during wear. Polyethylene (PE) and polyvinyl chloride (PVC) can provide reasonable cushioning and shock absorption but polyethylene (PE), like ethylene vinyl acetate (EVA), suffers high permanent compression set. Latex rubber foams tend to be too soft and “bottom out” under low loads—they offer little cushioning or shock absorption and they primarily serve to cosset the foot. Polyurethane (PU) foam and viscoelastic polyurethane's (PUs) offer good cushioning and shock absorption properties. However, polyurethane's (PUs) can be bulky, lose their properties when wet and are susceptible to creep and fatigue degradation which involves the increase in deformation with time under constant stress, thereby rendering them ineffective. See FIG. 3, which summarizes the material characteristics of conventional shoe insole materials.

Polymeric insoles have been investigated for the immediate shock-attenuation abilities of new cushioned insoles. The material degradation that occurs with regular use influences the effectiveness of the insoles. A study found that insoles constructed with polyurethane foam underwent a significant deterioration in shock-absorbing ability after a few weeks of daily walking. Another study, however, found that cushioned insoles made of polyeurethane foam with an ethylene vinyl acetate (EVA) heel cup maintained their shock-attenuation abilities throughout 18 weeks of military training. In both studies it becomes clear that, eventually, there is a significant deterioration in shock-absorbing abilities over time as the polymeric structures degrade.

Knitted and/or woven spacer fabrics which are elastic in structure are known and have been employed in various applications, such as in clothing, mattresses, seats, and patient support material in the medical industry.

A three-dimensional knit spacer fabric includes a first fabric layer, a second fabric layer and yarns interconnecting the two fabric layers. Some of the yarns interconnecting the two fabric layers are perpendicular to each of the first and second fabric layers, while the remaining interconnecting yarns are disposed at an angle between the two fabric layers. See FIG. 4, which shows a spacer fabric 30 having a first fabric layer 35, a second fabric layer 40, and a plurality of interconnecting yarns 45 extending between the first and second fabric layers 35, 40.

The double-face spacer fabric is prepared by knitting a three-dimensional knit fabric on a double-needle bar warp knitting machine commonly used in the manufacture of velvet. In preparing the three-dimensional spacer fabric knit, the yarn that is used is a synthetic material such as polyester, acrylic or nylon. The yarn may be filament or spun, textured or fully oriented. The yarn interconnecting the two fabric layers of the spacer fabric should have sufficient resilience and stiffness to keep the two fabric layers apart even if pressure is applied to either one of the two fabric layers in the construction.

The interconnecting pile yarns (which extend between the two fabric layers) can be made of the same or a different material from that of the two fabric layers. In order to render the interconnecting pile yarns resilient, the yarns may be made of a resilient material such as a monofilament or multifilament polyester or nylon.

In 1995 Robert Spillane invented the use of spacer fabrics, made of monofilament yarn or polyester fibers, for the insole of an athletic shoe. See U.S. Pat. No. 5,385,036. More recently, in International (PCT) Patent Application Publication No. WO/2011/155824, there is disclosed a shoe insole which includes a knitted spacer fabric made of monofilament and polymeric yarns with a diameter of between 0.09 mm and 0.12 mm. In both disclosures, the fibers are monofilament yarns which are a single filament of a synthetic fiber which is strong enough to be useful without being twisted with other filaments into a yarn. These monofilament yarns are made from common textile polymers such as polyester, Nylon 6, Nylon 66, high density polyethylene (HDPE), polypropylene and polybutylene terephthalate (PBT). Despite the spacer fabric itself being compressible, these constituent materials are also susceptible to compression under the load of a person walking, and hence are believed to provide nominal shock-absorbing and pressure-distributing functions. It is believed that insoles formed of spacer fabrics have not been commercialized for this reason.

Spacer fabric insoles are constructed to be light and have a high value of ventilation in comparison to foam and gel materials. Air can flow between the top and bottom fabric layers through the interconnecting fibers, which can also wick away moisture and either cool or insulate the foot. See FIG. 5, which shows how the three discrete layers of the spacer fabric can provide a light, breathable, wicking and cooling/insulating construct.

The density of shoe insoles is measured in accordance with DIN 53479. Water vapor permeability is tested in accordance with ISO 20344/14268. Water vapor absorption is measured in accordance with ISO 20344/17229. The breathability of the insole material is measured in accordance with ISO 7231.

The disadvantage to polymeric spacer fabrics such as disclosed in U.S. Pat. No. 5,385,036 and International (PCT) Patent Publication No. WO 2011/155824 is that plastics are relatively weak, and are prone to creep, fatigue degradation and permanent compression set. When a plastic material is subjected to a constant load, it deforms continuously. The initial strain is roughly predicted by its stress-strain modulus. The plastic material will continue to deform slowly with time, either indefinitely or until rupture or yielding causes failure, i.e., a permanent set. The primary region of the stress/strain curve is the early stage of loading, when the creep rate decreases rapidly with time. Then it reaches a steady state, which is called the secondary creep stage, followed by a rapid increase (i.e., the tertiary stage) and fracture. This phenomenon of deformation under load with time is called creep. Some materials do not have a secondary stage, while tertiary creep only occurs at high stresses and for ductile materials. All plastics creep to a certain extent. The degree of creep depends on several factors such as the type of plastic, whether the material is wet or dry, the magnitude of the load, the cyclical load rate, the temperature and time. The standard test method for creep characterization is ASTM D2990.

In any case, insoles formed out of spacer fabrics have proven unsatisfactory in practice.

SUMMARY OF THE INVENTION

Shoe insoles and foot orthotics that have cushioning properties have conventionally been made of materials such as gels, elastomers or foams in order to achieve the desired dampening/cushioning properties within the thickness limitations dictated by the constraints of commercially available shoes, sneakers and boots. While acceptable cushioning properties may be obtained initially, over time such elastomeric or foam material insoles are compressed during use, causing them to lose their shape. Insoles made of elastomeric or foam materials have proven uncomfortable and ineffective to users over extended periods of use by failing to provide sufficient support and/or cushioning. Spacer fabrics made of monofilament yarn, polyamide or polyester fibers have been used for the insole of an athletic shoe and/or the sole of ski boot. The knitted spacer fabric comprises a top layer, a bottom layer, and a plurality of spacing threads extending between the top layer and the bottom layer. However, these polymer spacer fabrics are weak and can easily be crushed without elastic recovery. For this reason, polymer spacer fabrics are not used today for insoles because they have a tendency to deform permanently under the influence of stresses (standing, walking, running), a phenomenon in material science frequently referred to as “creep”. All plastics creep to a certain extent. For this reason, in shoes and sneakers, spacer fabrics are typically employed in non-weight bearing structures such as side walls, metatarsal regions and tongues.

The present invention relates to a shoe insole and foot orthotics made of three-dimensional spacer fabrics produced out of metallic shape memory materials (SMM), e.g., Nitinol, which are substantially stronger than the polymer monofilaments used today and which are not susceptible to deleterious creep which often renders polymeric insoles and orthotics useless. The novel shape memory material (SMM) spacer fabric constructs can be shape set to a specific foot geometry, supply improved dampening/cushioning and offer superelastic shape recovery to ensure long-lasting support. See FIG. 6, which shows a novel three dimensional spacer fabric 50 formed out of a shape memory material (e.g., Nitinol), wherein spacer fabric 50 comprises a first layer 55, a second layer 60 and a plurality of interconnecting filaments 65 extending between the first and second layers 55, 60.

In one preferred form of the invention, there is provided a shoe insole comprising:

a spacer fabric comprising a bottom layer, a top layer, and a plurality of interconnecting filaments extending between said bottom layer and said top layer;

wherein at least one of said bottom layer, said top layer and said plurality of interconnecting filaments comprise a shape memory material.

In another preferred form of the invention, there is provided a shoe upper comprising:

a spacer fabric comprising a bottom layer, a top layer, and a plurality of interconnecting filaments extending between said bottom layer and said top layer;

wherein at least one of said bottom layer, said top layer and said plurality of interconnecting filaments comprise a shape memory material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein:

FIG. 1 is a schematic view showing insoles made of a compressible polymer;

FIG. 2 is a schematic view showing an insole with custom cushioning for different regions of the foot;

FIG. 3 is a schematic view showing shoe insole material characteristics;

FIG. 4 is a schematic view showing a spacer fabric, with the spacer fabric being compressed;

FIG. 5 is a schematic view showing how three-dimensional spacer fabrics comprise multiple discrete layers, are lightweight, breathable, will wick away moisture and will cool or insulate;

FIG. 6 is a schematic view showing a spacer fabric made from shape memory material;

FIG. 7 is a schematic view showing a spacer fabric made from Nitinol;

FIG. 8 is a schematic view showing the stress-strain curves for steel and Nitinol;

FIG. 9 is a schematic view showing the damping capacity of Nitinol, aluminum, stainless steel and brass as a function of temperature;

FIG. 10 is a schematic view showing the storage modulus capacity of Nitinol, aluminum, stainless steel and brass as a function of temperature;

FIG. 11 is a schematic view showing how superelastic spacer fabrics can be layered on top of each other;

FIG. 12 is a schematic view showing the various regions of the sole of a foot;

FIG. 13 is a schematic view showing pressure distribution under a patient's foot;

FIG. 14 is a schematic view showing a mold used to generate a custom orthotic;

FIG. 15 is a schematic view showing the stress-strain diagram for bone, Nitinol and stainless steel;

FIG. 16 is a schematic view showing the formation of stress-induced martensite; and

FIG. 17 is a schematic view showing the shore hardness scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, and looking now at FIG. 7, there is provided a new and improved three dimensional spacer fabric construct 50 made of a shape memory material (SMM) such as Nitinol. The shape memory material (SMM) spacer fabric construct 50 comprises a first layer 55, a second layer 60 and a plurality of interconnecting filaments 65 extending between the first and second layers 55,60. The superelastic vertical “fibers” (filaments) 65 create the elastic response in the insole and/or orthotic when compressed by the foot, made to bend, collapse and allowed to shape recover, which addresses the deficiencies of the prior art.

With shape memory metals such as Nitinol, pseudoelasticity, sometimes called superelasticity, is an elastic (reversible) response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal. Pseudoelasticity (superelasticity) is from the reversible motion of domain boundaries during the phase transformation, rather than just bond stretching or the introduction of defects in the crystal lattice (thus it is not true superelasticity, but rather pseudoelasticity). Even if the domain boundaries do become pinned, they may be reversed through heating. Thus, a pseudoelastic material may return to its previous shape (hence, “shape memory”) after the removal of even relatively high applied strains. One special case of pseudoelasticity is called the Bain Correspondence which involves the austenite-to-martensite phase transformation between a face-centered crystal lattice and a body-centered tetragonal crystal structure.

Superelastic alloys belong to the larger family of shape memory alloys. When mechanically loaded, a superelastic alloy deforms reversibly to very high strains—up to 10%—by the creation of a stress-induced phase. When the load is removed, the new phase becomes unstable and the material regains its original shape. Unlike shape memory alloys that utilize shape memory effect, in superelasticity no change in temperature is needed for the alloy to recover its initial shape. Superelastic devices take advantage of their large, reversible deformation. Superelastic products include antennas, eyeglass frames and biomedical stents.

Among other things, the present invention provides a dynamic insole and/or foot orthotic made of metallic shape memory material that has vastly improved fatigue life compared to polymeric alternatives. Metal and polymeric fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loadings. Metals and polymers are different in the fact that polymers are viscoelastic and commonly show hysteretic elastic effects, whereas most metals tend to have only linear elastic behavior. Yet the relationship between stress or strain amplitude and fatigue life are asserted for polymers in the same way as for metals. Most polymeric materials exhibit vastly less endurance fatigue levels compared to structural metals, i.e., steel, stainless steel, titanium and Nitinol (a nickel-titanium alloy).

It is the polymer's hysteretic elastic effects that make the polymer spacer fabric structure so resilient to compressive set, but polymers are weak compared to the forces encountered in shoe insole and orthotic applications. While in most engineering materials load increases with deflection upon loading in a linear way, and decreases along the same path upon unloading, shape memory metals, e.g., Nitinol, exhibit a distinctly different behavior—it has a hysteretic elastic behavior like weak polymers but also has the large strength of metals.

In Nitinol, upon loading, stress first increases linearly with strain up to approximately 1% strain. After a first “yield point”, several percent strain can be accumulated with only a small stress increase. The end of this plateau (“loading plateau”) is reached at about 8% strain. After that, there is another linear increase of stress with strain. Unloading from the end of the plateau region causes the stress to decrease rapidly until a lower plateau (“unloading plateau”) is reached. Strain is recovered in this region with only a small decrease of stress. See FIG. 8.

Nitinol exhibits a hysteresis stress-strain curve allowing for 8% shape recovery before permanent set, which is unique for metals but common in polymers. The last portion of the deforming strain is finally recovered in a linear fashion again. The unloading stress can be as low as 25% of the loading stress. For comparison, the straight line representing the linear elastic behavior according to Hook's law for steel is also shown in FIG. 7. Nitinol has a hysteresis stress-strain curve similar to polymers. However, when the spacer fabric is made of Nitinol it can support heavy loads, eventually deflect under these weight-bearing loads and cushion the loads, and then recover its shape when the loads are removed.

In one preferred form of the present invention, the Nitinol spacer fabric has enhanced cushion energy (CE), cushion factor (CF) and resistance to dynamic compression compared to polymer spacer fabrics when tested per SATRA's cushion testing protocol (June, 1992, pages 1-7). Cushion energy (CE) is the energy required to gradually compress a specimen of the material up to a standard pressure with a tensile-compression testing machine. Cushion factor (CF) is a bulk material property and is assessed using a test specimen greater than sixteen millimeters thick. The pressure on the surface of the test specimen at a predefined loading is multiplied by the volume of the test specimen under no load. This pressure is then divided by the cushion energy of the specimen at the predefined load. Lastly, the resistance to dynamic compression measures changes in dimensions and in cushion energy after a prolonged period of dynamic compression.

And in one particularly preferred form of the present invention, the spacer fabric insoles and orthotics comprise a shape memory material (e.g., Nitinol) that is kink resistant. Unlike most metals, Nitinol wires have a unique quality of being kink resistant. These wires can be bent 10 times more than stainless steel wire without permanent deformation. For example, a 0.035″ Nitinol wire can be wrapped around a 0.50″ diameter mandrel without taking a set, while a stainless steel wire of the same diameter can only be bent around a 5″ diameter mandrel without being plastically deformed.

Kink resistance is an important feature of Nitinol for spacer fabrics produced on the double bar knitting machines. Most metals will not allow for tight radii bending during knitting without kinking, but Nitinol does. In the present application, Nitinol spacer fabric insoles and orthotics can be completely compressed (crushed) flat and will return to their original height when the deforming force is removed without kinking. Other structural metals such as steel, stainless steel and titanium will kink.

In another preferred form of the present invention, the Nitinol spacer fabric has enhanced dampening and cushioning characteristics compared to other metals, and even polymers, by exploiting the shape memory material's unique ability to recover large strains due to a solid-solid phase transformation and to dissipate energy because of the resulting internal friction. It is known that the high damping capacity of the thermoelastic martensitic phase of Nitinol is related to the hysteretic movement of interfaces in the alloy (martensite variant interfaces and twin boundaries). Also, the damping capacity of shape memory material (SMM) depends directly on external variables such as heating rate, frequency and oscillation amplitude; and internal variables such as the type of material, grain size, martensite interface density and structural defects. In Nitinol, a high damping capacity and a low storage modulus in the martensitic state is observed. It has been verified that during phase transformation, there is the presence of a peak in damping capacity and an equivalent increase of storage modulus. The storage modulus, represented by the elastic component and related to a material's stiffness.

A comparative study on the dynamic properties of structural materials was carried out and clearly demonstrates the superior damping behavior of the shape memory alloy (SMA) Nitinol over classical structural materials under the same external conditions. Among other things, Nitinol (NiTi) SMA specimens were compared to commercial aluminum, stainless steel and brass as samples of classical materials. All beam specimens were submitted to Dynamic Mechanical Analysis (DMA) tests using a commercial apparatus in a single cantilever mode under temperature variation. Damping capacity and storage-modulus variation were analyzed.

Dynamic modulus is the ratio of stress to strain under vibratory conditions calculated from data obtained from either free or forced vibration tests, in shear, compression, or elongation. It is a property of viscoelastic materials. The storage and loss modulus in viscoelastic solids measure the stored energy, representing the elastic portion, and the energy dissipated as heat, representing the viscous portion. Damping behavior of all specimens were observed, with the NiTi SMA, aluminum, stainless steel and brass specimens being submitted to a temperature ramp of 5° C./min with a frequency of 1 Hz and 5 μm of oscillation amplitude. See FIG. 9.

The NiTi SMA showed, in the martensitic state (between room temperature and about 70° C.), a higher damping capacity in comparison with the other studied materials. This difference in damping capacity increases even more in the phase transformation temperature range (between 70° C. and 90° C.), when the NiTi specimen presents a significant peak in its damping capacity, while aluminum, stainless steel and brass samples present relatively modest, incremental increases in their damping capacities. For temperatures higher than 90° C., the NiTi SMA is fully in the austenitic state, which intrinsically presents smaller energy absorption than the martensitic state. The fact that the NiTi SMA alloy is in its fully austenitic state explains the decrease in its damping capacity in this temperature range, as compared to the NiTi SMA alloy when it is in its martensitic state. Better damping capacity values can also be obtained from the NiTi SMA as the oscillation amplitude and/or frequency decrease and as the heating rate increases. The storage modulus variation is better visualized in relation to room temperature—while a reduction of 5% is perceived in classical materials, a clearly superior increase of about 17% occurs in NiTi SMA. See FIG. 10.

The nickel-titanium ratio of Nitinol can be modified to lower the phase transformation temperature to keep the material martensitic between freezing and 90° C.

This comparative study has shown the high damping capacity of NiTi SMA in the martensitic state and during phase transformation. Even better damping values can be obtained from NiTi SMA as the oscillation amplitude, frequency and heating rate varies. The study also showed a significant increase in storage modulus during phase transformation.

Nitinol can be very useful when designing a spacer fabric that requires stiffness control, since the phase transformation is reversible. By contrast, classic structural materials (e.g., stainless steel, aluminum, brass, etc.) present an almost-linear increase in damping capacity and similar decrease in storage modulus. Other metals and polymers do not have this unique phase transformation and will not afford the spacer fabric construct improved storage modulus due to a shock-absorbing attenuation from its hysteresis.

Thus, in one preferred form of the invention, the novel shoe insole is constructed out of a shape memory material which is engineered to oscillate between phase transformations so as to maximize its peak dampening characteristics and storage modulus.

Further details of the present invention are described below.

Spacer Fabric

Spacer fabrics are two separate fabric faces which are knitted independently and then connected together by a separate filler spacer fiber. These nonwoven fabrics can be produced on both circular and flat knitting machines. They may be produced as a flat sheet, or as a cylindrical tube.

Spacer fabrics have three distinct layers. The three ply structure has good breathability, wettability, crush resistance, and a 3D porous appearance. Each layer can be made of different materials and have different porosity levels and geometry. These spacer fabrics can be stacked on one another so as to form a multi-level spacer fabric construct which can be useful when needing to support a large arch in the foot or if more cushion energy (CE), cushion factor (CF) and resistance to dynamic compression is required. See FIG. 11, which shows a multi-level spacer fabric construct 70 comprising a first layer 55, a second layer 60, a plurality of interconnecting filaments extending between the first and second layers 55, 60, a third layer 75, a fourth layer 80, and a plurality of interconnecting filaments extending between the third and fourth layers 75, 80, etc.

The spacer fabric can be designed to have an overall porosity ranging from 45% to 98%, with pore sizes ranging from 100-600 microns (0.004-0.02 in.), and an average of 300 microns (0.01 in.). The modulus of elasticity of this stand-alone material can be engineered to have a modulus between 25 and 100 kN/m. It can have a Shore A hardness between 20 and 100. In a drop weight test, using an 18 kg weight, the material can experience a maximum force between 0.5 and 1 kN. The material can be designed to deform by 5 to 20 mm under this load while absorbing greater than 50% of the impact energy.

Clinical Issues

There are many anatomic biomechanical deficiencies of a foot that can be identified by a foot specialist: flat feet, raised arch, Morton's neuroma, foot inversion, foot eversion, hammer toes, corns, calluses, heel pain, plantar fasciitis, heel spur syndrome, etc. Some of these deficiencies may be interrelated. For example, a raised arch may cause other problems such as corns, calluses or heel pains inasmuch as walking pressure is not properly distributed as compared to a normal foot. Other problems such as hammer toes may be caused by the type of footwear that is used, such as high heels or very tight shoes. Furthermore, foot deficiencies may also cause problems or deficiencies in other parts of the body, particularly in the legs and the back of a person. FIG. 12 shows various regions about the sole of the foot.

Pressure mapping is a common method used by physicians to identify foot problems. The patient stands on a pressure map which generates a scan of the pressure distribution of the patient's ground-foot interface. This can be a static test, where the patient stands still on the pressure map, or dynamic where the patient walks over the pressure map. In the static condition, this provides information on pressure distribution and loading characteristics of the foot. In the dynamic condition, this provides gait analysis along with pressure distribution information. Regions of high pressure may lead to foot pain. An orthotic device may be used to alleviate this foot pain by properly distributing the pressure over a larger area (i.e., by providing additional support). See FIG. 13, which shows exemplary pressure distribution under a patient's foot.

Traditionally, if pressure mapping reveals regions of high pressure, custom orthotics may be prescribed for the patient. These orthotics are designed to more evenly distribute the load at regions of the foot where high pressure zones are observed. A 3D scan of the foot is taken to generate a computer-based solid model of the foot. To do this, the patient may step into a foam mold, which deforms around the foot. This foam mold is then scanned by a laser to generate a model of the foot. Alternatively, the patient may stand on a bed of pins which deform around the geometry of the foot. The computer measures how much each pin moves, and uses this information to generate a model of the foot. See FIG. 14, which shows a foot mold which may be used to generate a custom orthotic.

The computer model forms the basis for the orthotic geometry. The physician can edit the geometry to increase support in specific regions of the foot. This computer model is then transferred to casting and milling machines which create the orthotic using this digital geometry. This process can take several weeks, involve multiple trips to the physician's office, and may cost more than $500 for a pair of orthotics.

Novel Superelastic Spacer Fabric Insole/Orthotic

A superelastic spacer fabric insole/orthotic addresses many of the problems current insoles do not adequately address, namely, inadequate mechanical and fatigue strength. Additionally, custom orthotics may be prohibitively expensive and are labor intensive to produce.

Spacer fabrics have been in production for many years, and have been extensively used in the footwear industry; however, they have always been made of polymeric materials (which suffer from the deficiencies discussed above). The present invention, which comprises a Nitinol spacer fabric manufactured from a superelastic metallic wire, offers many advantages compared to polymeric materials.

Like a polymeric spacer fabric, the superelastic spacer fabric of the present invention can be engineered to have extra thickness in certain regions, may be multi-ply, offering improved cushion energy (CE), cushion factor (CF), and resistance to dynamic compression in certain regions of the insole or orthotic, e.g., in the metatarsal, heel, and Morton's areas. Unlike the polymeric materials used today, a metallic superelastic spacer fabric will avoid kink, creep, fatigue and compressive set, thereby allowing the insole/orthotic structure to functionally last much longer than, and perform much better than, a polymer spacer fabric.

Shape memory materials such as Nitinol possess additional properties that may be beneficial when used as the raw material for a spacer fabric. A Nitinol spacer fabric is superelastic (SE), meaning that if it is deformed, it is capable of returning to its original shape once the deforming force is removed. Additionally, a Nitinol spacer fabric can exhibit a shape memory effect (SME), meaning that it can be dynamic under the influence of temperature change, e.g., body temperature. As an example of an SME application, the dynamic insole can in a compressed state at a temperature below body temperature (37° C.), and, after the shoe is put on, the heat from the foot causes the Nitinol spacer fabric to expand, filling any voids between the insole and the foot, and applying pressure against the foot so as to help distribute pressures while providing additional support.

A Nitinol spacer fabric insole is also advantageous when used for custom orthotics. Instead of having to scan a patient's foot geometry and custom machine the custom orthotic, a custom Nitinol orthotic can be made by shape setting the Nitinol spacer fabric. In one example of this, the patient steps onto a bed of stainless steel pins, deforming the stainless steel pins to the geometry of the foot. The bottom of the stainless steel pins presses against the Nitinol spacer fabric, deforming the Nitinol spacer fabric to the shape of the foot. The stainless steel pins can then be locked into place against the Nitinol spacer fabric, and the patient's foot removed. The deformed spacer fabric can then be heated to 450° C. for 2 minutes and quenched so that, when the stainless steel pins are removed, the spacer fabric will permanently hold this shape. The heating to shape-set the Nitinol spacer fabric can also be accomplished by applying a current to the Nitinol spacer fabric and heat it through resistive heating effects. This represents a much more rapid and cost effective method for producing custom orthotics.

Nitinol is characterized by a specific stress-strain diagram that is different from the deformation behavior of conventional materials. Typical stress-strain diagrams for stainless steel, Nitinol (“NiTi alloy”), and living tissues are illustrated in FIG. 15. In the case of stainless steel, the elastically recovered strain (i.e., the linear portion of the curve) is lower than 0.5%. Once the elastic limit is exceeded, stainless steel yields (dislocation slip) and considerable increase in strain is achieved. This increase in strain, where the metal appears to flow like a viscous liquid, is called plastic deformation and allows the materials to acquire a permanent set that cannot be recovered after the stress is released.

In shape memory materials (SMMs) like Nitinol, early deformation is also linearly proportional to the applied stress. Thereafter, deformation continues without a significant increase in the force (i.e., the upper loading plateau of the curve). During unloading, the constraining force is again constant over a wide range of shapes (the unloading plateau of the curve). Up to 8% deformation is recoverable in Nitinol. When Nitinol (NiTi) used as a spacer fabric, the structure can recover up to 100% of its shape after being compressed.

Polyester is a typical polymeric material used in spacer fabrics. Polyester has a stiffness of 2 GPa, and a tensile strength of 80 MPa. Nitinol has vastly superior mechanical properties to polyester—Nitinol has an austenitic modulus of 83 GPa, and an austenitic tensile strength of 690 MPa. While Nitinol can form a weaker stress-induced martensite phase at approximately 400 MPa (58,000 PSI), this load would far exceed any load seen in a shoe insert. It is possible to engineer the Nitinol spacer fabric construct so that its superelastic regime toggles between the martensite and austenite phases for enhanced dampening characteristics. See FIG. 16.

The diameter of the starting fiber greatly determines the mechanical properties of the final spacer fabric structure. Thicker fibers result in a stiffer final spacer fabric construct. The upper limit for the fiber diameter is determined by the knitting machine being used. Preferably, the diameter of the superelastic fiber is between 0.05 in and 0.0002 in. Most preferably, the superelastic fiber is between 0.01 in and 0.003 in.

In addition to, and/or in combination with, Nitinol, other shape memory metals can be used to form the superelastic spacer fabric, along with shape memory polymers (e.g., thermoplastic block copolymers).

The superelastic spacer fabric has three distinct layers which can be manufactured using three distinct wire sizes. By way of example but not limitation, a fine wire size may be used for the top and base of the Nitinol spacer fabric so as to increase the smoothness and to reduce the friction between the foot and the insole. A thicker wire may be used for the vertical, filler material (i.e., the interconnecting filaments extending between the top and base layers) so as to give the structure more robust stiffness and elasticity.

The Nitinol spacer fabric can also be impregnated with a gel, such as a silicone gel, and/or other various polymeric materials. The metallic spacer fabric acts as a spring, absorbing the energy imparted through the insole during movement (e.g., walking or running). The Nitinol spacer fabric also provides cushioning, by supporting the surface area of the foot. The gel material (or other impregnating material) acts as a damper, dissipating this energy efficiently. The Nitinol spacer fabric can give support to the gel (or other impregnating material) so as to increase its stiffness and fatigue endurance limit and can be viewed as somewhat analogous to the use of rebar and mesh in concrete. The gel (or other impregnating material) can be made with Shore 00 hardness of 30 (Extra Soft) to a Shore D hardness of 30 (Hard). See FIG. 18. Additionally, impregnating the insole with the gel or other material keeps the individual wires of the Nitinol spacer fabric in place. Thus, if an insole should be cut during use, fraying of the Nitinol spacer fabric can be mitigated.

Alternatively, a polymeric material that exhibits a solid-to-viscous fluid transition under applied load can be used to impregnate the spacer fabric. One example of such a polymer is Ultra High Molecular Weight Polyethelyne (UHMPE). Energy from the impact of taking a step is absorbed by the solid UHMPE. The peak force of taking a step causes the solid UHMPE to undergo a phase change and become liquid. The energy from the loading of the insole is absorbed by the UHMPE, and the wearer experiences increased cushioning from this effect. When the insole is unloaded, the liquid UHMPE reverts back to the solid state, and is ready for the next loading cycle.

The Nitinol spacer fabric can be coated with a thin layer of silver to impart antifungal and antibacterial properties. In one preferred embodiment of the invention, the silver is electrochemically coated onto the Nitinol spacer fabric. Alternatively, the layer of silver can be deposited using a chemical or physical vapor deposition method.

The silver coating can also be applied to the Nitinol wire before Nitinol wire is knit into the spacer fabric construct. The Nitinol wire can be plated with silver using one of the aforementioned techniques. Alternatively, the silver-coated Nitinol wire can be created by drawing a metal on metal composite (e.g., a Nitinol core and a silver outer tube) so as to create the final silver-coated Nitinol wire.

Use Of Nitinol Spacer Fabric To Form Shoe Upper

If desired, it is also possible to form the shoe upper out of a superelastic spacer fabric. Such a construction can be desirable, since the shoe upper can be highly elastic, thereby eliminating a sense of compression on the top of the foot and reducing fatigue. In addition, forming the shoe upper out of superelastic spacer fabric can reduce shoe weight, enhance breathability, enhance moisture wicking, and can provide increased cooling or insulation.

Modifications Of The Preferred Embodiments

It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention. 

What is claimed is:
 1. A shoe insole comprising: a spacer fabric comprising a bottom layer, a top layer, and a plurality of interconnecting filaments extending between said bottom layer and said top layer; wherein at least one of said bottom layer, said top layer and said plurality of interconnecting filaments comprise a shape memory material.
 2. A shoe insole according to claim 1 wherein said shape memory material is superelastic.
 3. A shoe insole according to claim 2 wherein said shape memory material is Nitinol.
 4. A shoe insole according to claim 2 wherein said shape memory material is a Titanium near-beta alloy.
 5. A shoe insole according to claim 1 wherein said plurality of interconnecting filaments comprise a shape memory material.
 6. A shoe insole according to claim 5 wherein said plurality of interconnecting filaments comprise a shape memory material and wherein at least one of said top layer and said bottom layer do not comprise a shape memory material.
 7. A shoe insole according to claim 5 wherein wherein said bottom layer, said top layer and said plurality of interconnecting filaments all comprise a shape memory material.
 8. A shoe insole according to claim 1 wherein said shape memory material is engineered to have a martensitic state between 0 degrees C. and 90 degrees C.
 9. A shoe insole according to claim 1 wherein the shape memory material is engineered to oscillate between phase transformations so as to maximize its peak dampening characteristics and storage modulus.
 10. A shoe insole according to claim 1 wherein said shoe insole is contoured so as to provide increased support to specific regions of a user's foot
 11. A shoe insole according to claim 10 wherein said contouring is achieved by shape-setting said shoe insole using a heating source.
 12. A shoe insole according to claim 1 wherein voids in said spacer fabric are filled with a material.
 13. A shoe insole according to claim 12 wherein said material is a gel.
 14. A shoe insole according to claim 12 wherein said material comprises a polymer capable of transitioning between a solid state and a viscous state due to loading and unloading of said shoe insole.
 15. A shoe insole according to claim 1 wherein said shape memory material is coated with silver to impart antibacterial and antifungal properties to said shape memory material.
 16. A shoe insole according to claim 1 wherein said shoe insole comprises an orthotic.
 17. A shoe upper comprising: a spacer fabric comprising a bottom layer, a top layer, and a plurality of interconnecting filaments extending between said bottom layer and said top layer; wherein at least one of said bottom layer, said top layer and said plurality of interconnecting filaments comprise a shape memory material.
 18. A shoe upper according to claim 17 wherein said shape memory material is superelastic.
 19. A shoe upper according to claim 18 wherein said shape memory material is Nitinol.
 20. A shoe upper according to claim 17 wherein said plurality of interconnecting filaments comprise a shape memory material.
 21. A shoe upper according to claim 20 wherein wherein said bottom layer, said top layer and said plurality of interconnecting filaments all comprise a shape memory material.
 22. A shoe upper according to claim 17 wherein said shape memory material is engineered to have a martensitic state between 0 degrees C. and 90 degrees C.
 23. A shoe upper according to claim 17 wherein the shape memory material is engineered to oscillate between phase transformations so as to maximize its peak dampening characteristics and storage modulus.
 24. A shoe upper according to claim 17 wherein voids in said spacer fabric are filled with a material.
 25. A shoe upper according to claim 17 wherein said shape memory material is coated with silver to impart antibacterial and antifungal properties to said shape memory material. 